RDM (lighting)

Remote Device Management or RDM is a protocol enhancement to USITT DMX512 that allows bi-directional communication between a lighting or system controller and attached RDM compliant devices over a standard DMX line. This will allow configuration, status monitoring, and management of these devices in such a way that does not disturb the normal operation of standard DMX512 devices that do not recognize the RDM protocol. The standard was originally developed by the Entertainment Services and Technology Association - Technical Standards (ESTA) [1] and is officially known as "ANSI E1.20, Remote Device Management Over DMX512 Networks.

As of January 2011 ESTA, the Entertainment Services and Technology Association in North America, has merged with the Professional Lighting and Sound Association, a similar organization in the UK. The new organization is called PLASA. [2] All ESTA standards are now maintained by PLASA.

The RDM protocol and the RDM physical layer were designed to be compatible with legacy equipment. All compliant legacy DMX512 receivers should be usable in mixed systems with an RDM controller (console) and RDM responders (receivers). DMX receivers and RDM responders can be used with a legacy DMX console to form a DMX512 only system. From a user’s point of view the system layout is very similar to a DMX system. The controller is placed at one end of the main cable segment. The cable is run receiver to receiver in a daisy-chain fashion. RDM enabled splitters are used the same way DMX splitters would be. The far end (the non console or splitter end) of a cable segment should be terminated.

RDM requires two significant topology changes compared to DMX. However, these changes are generally internal to equipment and therefore not seen by the user.

First, a controller’s (console’s) output is terminated. Second, this termination must provide a bias to keep the line in the ‘marking state’ when no driver is enabled.

The reason for the additional termination is that a network segment will be driven at many points along its length. Hence, either end of the segment, if unterminated, will cause reflections.

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